1. Field Of The Invention
The present invention relates to a car interval control apparatus which controls the distance between a car driven by a driver and a car running ahead of or preceding the driver's car.
2. Discussion of Background
There have been proposed car interval control apparatuses for controlling a car interval in publications such as Japanese Examined Patent Publication Nos. 4700/1986 and 6349/1986. In such prior-art techniques, radio waves or light is used to measure the car interval. An example of measuring the car interval is shown in FIG. 4 wherein emitted light is caused to reflect by an object to be measured 9 and a time required for reciprocation of the light is measured.
The car interval control apparatus as shown in FIG. 4 comprises a car interval range finder 1, a throttle actuator 2 to control the output of the engine, a brake actuator 3 to control the brake of the car, a control unit 4, a set switch 5, a brake switch 6 and a car speed sensor 7.
The operation of the car interval control apparatus as shown in FIG. 4 will be described.
When the driver turns on the set switch 5 of the car interval control apparatus, the control unit 4 reads the car speed at that time from the car speed sensor 7 and calculates a car interval which is considered to be safe. When the distance between the driver's car and a preceding car measured by the range finder 1 is larger than the distance considered to be safe obtained by the calculation in the control device 4, the car is driven at the speed when the set switch was turned on. However, when the former distance is shorter than the latter distance, the car is decelerated by the actuation of the throttle actuator 2 to thereby reduce the output of the engine. When the distance between the driver's car and the preceding car becomes small in spite of the actuation of the throttle actuator 2, the control unit 4 actuates the brake actuator 3 so that the car is further decelerated to thereby keep a safe car-interval distance from the car 9. The conventional car interval control apparatus thus described has, however, a disadvantage that the range finder 1 can not discriminate whether the reflected waves or light come from the preceding car or they come from an object at a road side.
There has been proposed a car interval control apparatus using a tracking method which is disclosed in a Publication such as Japanese Examined Patent Publication No. 33352/1985. In this car interval control apparatus, a window 10 is formed in a picture image formed by an image sensor and shown on a display screen. Then, the picture of a car is provided in the window 10 at the time of t=t.sub.0 as shown in FIG. 5a. A picture image which most resembles the picture image in shape and size is determined from picture images at the time of t=t.sub.0 +.DELTA.t (as shown in FIG. 5b), and a new window 10 is set for the newly determined picture image. By conducting this operation in a time-sequential manner, the preceding car is tracked by forming the picture image in the window 10.
The above-mentioned conventional car interval measuring apparatus had, however, a disadvantage that it could not discriminate an object to be tracked and it simply measured the distance between the driver's car and an object (which may not be a car) ahead of the driver's car, and accordingly, it was not always able to measure the distance between the driver's car and a preceding car which runs ahead the driver's car, and therefore, it often caused an erroneous operation.
Further, the conventional car interval measuring device had a problem of safety. Namely, in a case that there was a car intervening at the front of the driver's car, most conventional cars were not able to detect an object close to but out of the forward center of the driver's car, so that the detection of the intervening car was delayed to thereby a potential danger.